1. Field of the Invention
The present invention generally relates to management of switched computer networks and, more particularly, to propagating detected changes in upstream connectivity to downstream devices.
2. Description of the Related Art
A computer network generally includes a number of devices, including switches, routers and hubs, connected so as to allow communication among the devices. The devices within a network may be generally categorized into two classes: end stations connected along the edge of a network and network devices. End stations typically include devices that primarily supply or consume information, such as workstations, desktop PCs, printers, servers, hosts, fax machines, and other such devices. Network devices typically include devices that primarily transfer information between other devices (e.g., between end stations and other network devices), such as gateways, switches, routers, and other such devices. In other words, network devices generally provide connectivity between end stations and the network core.
FIG. 1 illustrates an exemplary network 100 in which a plurality of end stations 110 are connected to a network core 120 via multiple layers of switches 130. In some cases, the network may be modeled in accordance with the Open System Interconnection (OSI) model, which defines a networking framework for implementing protocols in multiple (seven) layers. The switches 130 may represent Data Link or “Layer 2” layer switching, that encodes and decodes data packets into bits. Layer 2 switches implement the network transmission protocol and handle errors in the physical layer (Ethernet, optics, etc.), flow control and frame synchronization. In the illustrated example, switches 130 include aggregation switches 132 (SW1 and SW2), and access switches 134 (SW3 and SW4). The end stations 110 may be file servers, data servers, workstations, personal computers (PCs), and the like.
In an effort to provide greater reliability, such networks are often designed to provide redundant Layer 2 connectivity between end stations 110 and the network core 120. To this end, at least some end stations 110 may each have multiple network interface cards NICs 112 (or other type network interface/adapter), allowing the end stations 110 to connect to the network through primary links/connections (Lp) and secondary links (Ls). For example, the end stations may be configured to connect to the network through a primary path (via SW3 and SW1) by default and switch (or “failover”) to a secondary path (via SW4 and SW2) if a connectivity problem is detected in the primary path, such as a loss of connectivity to a link LC between switch SW1 and the network core 120.
In conventional systems, end stations do not become aware of a change in upstream connectivity until they discover it on their own. For example, end stations may only discover a loss of upstream connectivity after experiencing consistent protocol packet timeouts. As a result, after a loss in network connectivity on the primary path, end stations may not immediately switch from their primary path to their alternative path despite a loss in network connectivity on the primary path, which may degrade network performance.
Therefore, there is a need for techniques that cause end stations to switch over to alternative paths more rapidly in response to remote upstream connectivity changes.